Erm… League of Legends is not pay2win game, and it's not browser game either.
And on the top of it, it's not expensive. You don't need to pay a dime to get to the pro level. You need to train and you need a skill.

I've said already. I did buy ingame currency but didn't spend all of it - I have a stockpile of Riot Points that are just acidifying for two years. I did it only to support devs as I had years of fun with that game. Not only that, noone could win me by buying stuff. No, I'm not pro, I don't compete and am not interested into that stuff. I'm talking about blind normal matches where I play very good.

Oh and… I also have 200.000 of Influence Points and don't plan to use those. Yes I could go unlocking dozens of more champons, but I like the ones (50 of them) I have already and new ones are not nearly as interesting.

To find non pay2win browser MMO is probably impossible. I've tried and found none.
The last one was ogame before they've added dark matter in it. Didn't check The West lately, but the rumor is they've added Star Trek Online scandalous pay2gamble&win boxes/chests.

Quote from cracked.com - and you thought I'm the sole lunatic that just happened to preach bullshit on RPGwatch about Perferct World Entertainment. PWE is, lemme repeat it, one of the biggest scamming companies that exist on the planet!

Star Trek Online contains a fraud that should be banned from the whole internet as it's practically taxfree gambling if not one huge money laundry scheme. Sadly, it's not the only game that scams people this way and you'll find a similar stuff in many browser games, but also on phonegames (EA's Dragon Age phonegame is a perfect example).http://www.cracked.com/blog/6-ground…ewing-players/

Star Trek Online — Lock Box Keys

The lock box is a master-crafted psychological landmine. The game rewards you with a mysterious locked box, but you need to buy a key to get what's inside … which means you're really buying the item, with a side order of "duh" and the added advantage of not knowing what you're paying for. It's the Jedi mind trick in icon form, a little graphic saying "You have already bought this incredible item. Now go to the shop and pay for it." The most recent offender was Star Trek Online.

Most key buyers unlock one copy of an item they already have seven times, learn their lesson, and get on with the game. Lock boxes are the scratch cards of virtual warfare. Most players hate lock boxes, but hating is free, while the few people who like them spend lots of money, so screw everyone else while the system caters to the rich. And welcome to capitalism! A Starfleet officer asking for your credit card information is how you ruin immersion and a bold future utopia simultaneously.

They're unregulated gambling, simulated slot machines that aren't required to tell you the odds or ever pay out. Worse, the appeal of the lock box is a small chance of getting a rare and powerful item without earning it. Which means the best case scenario of this money sink is breaking the game.

Cryptic Studios
We all remember how the Federation was founded on greed and capitalism, right?